This invention relates to a manufacturing method and products of metallic friction materials, particularly to one reducing largely difficulty in manufacturing processes, needing low investment and productive cost.
Friction material is generally meant to such one used for moving or stopping a mechanical component, such as a clutch or a brake lining, etc. Early friction material included commonly asbestos, which has been found harmful to the environment and humane health, and gradually prohibited its use and replaced with other friction materials such as non-asbestos organic friction materials, semi-metallic, metallic friction materials. In a recent decade powder metallurgy has been developed greatly, and not a few commercialized products have been offered in market, utilizing technology of powder metallurgy. The present invention, metallic friction materials, is produced by utilizing powder metallurgy.
At present, many commercial friction materials (such as clutches, brake linings, etc.) are based on semi-metallic and metallic materials, the latter using technique of powder metallurgy, which includes: 1. preparing materials, 2. a process of making green bodies, 3. a process of proper heat treatment, and 4. micro-machining. The process of making green bodies is generally conducted at room temperature. The process of heat treatment is not merely to choose a proper temperature for sintering, the time needed, speed of raising temperature, etc., but also to control atmosphere during heat treating as an important point.
As for metallic friction materials, copper or iron alloys are mostly used, as disclosed in U.S. Pat. Nos. : 3,981,398, 4,311,524, 4,391,641, 4,415,363, 5,370,725 using iron-base friction materials.
The U.S. Pat. No. 3,891,398 uses an alloy made of nickel, copper, coke, graphite, silicon dioxide and alumina then formed under pressure of 200.about.300 MPa, then treated in 1000.degree. C. under reducing atmosphere for 15 minutes .about.3 hours, then cooled, finally densified under less than 800 MPa.
The U.S. Pat. No. 4,311,524 uses copper, tin, zinc sulphide, pyroceramic, graphite and lead etc. mixed in iron powder, formed by pressure under 294 MPa, then sintered at 1030.degree. C. for three hours under protected atmosphere of 1.96 MPa.
The U.S. Pat. No. 4,415,363 uses mainly iron, mixed with graphite, coke, tin, mullite, kyanite, silicon dioxide, steel wool and copper, formed under pressure coolly into green bodies under 411.6 MPa, treated at 700.about.1100.degree. C. under protected atmosphere for 30 minutes, then cooled and densified under 11.6 MPa.
The U.S. Pat. No. 5,370,725 produces iron synchronizer rings including: iron, carbon, copper, chromium, manganese, barium and phosphorus, formed into green bodies under 588 MPa, sintered at 1000.about.2000.degree. C. under controlled protected atmosphere for 80 minutes.
Further, U.S. Pat. Nos.: 4,050,620, 4,278,153, 4,394,275, 4,576,872, 4,871,394, 5,105,513, 5,125,962, 5,501,833 and 5,518,519 disclose copper-base abrasive materials.
U.S. Pat. No. 4,576,872 uses copper, tin, alumina, mica, graphite, lead, silicon dioxide, iron, nickel, chromium, titanium dioxide and steel fiber pressed to form green bodies under 482.23 MPa, and then sintered for 1 hour at 750.degree. C. under 0.15 MPa and protected atmosphere of 90% nitrogen and 10% hydrogen.
U.S. Pat. No. 4,871,394 uses copper powder mixed with silicon dioxide (or alumina), graphite, lead, tin and zinc, pressed to form green bodies of density 2.9.about.3.1 g/cm.sup.3, with a core plate pinched by two green bodies, and sintered for 1 hour at 650.degree. C. under 0.52 MPa protected in non-oxidizing atmosphere.
U.S. Pat. Nos. 5,501,833 and 5,518,519 use hard particles and copper-tin alloy ground into mixed powder, pressed to form green bodies under 392.about.588 MPa, sintered for 1 hour under nitrogen atmosphere, and then reshaped into annular friction material.
In the academic field, manufacturing friction material test samples and study about impact of wear characteristics of different ingredients and friction modes is always one of the important issues for discussion. Jamil made a systematic analysis and discussion in regard to friction materials of the copper system containing iron of 10% by wt., pressed to form green bodies under different pressures and sintered for 1 hour at 1140.degree. C. under protective atmosphere of 5H.sub.2 --N.sub.2.
Danninger discussed about the mechanical change of friction materials with vacancies (which produced in sintering process). The ingredients is made by the copper system containing iron of 3% by wt., having different particle sizes, pressed to form green bodies under 1200 MPa and 600 MPa, and then sintered for 2 hours at 1120.degree. C. and 1250.degree. C. under the protective atmosphere of hydrogen.
It is evident that the manufacture of copper-base or iron-base friction materials according to powder metallurgy has a process of sintering them in vacuum or under controlled protective atmosphere, whether disclosed in the patent field or the academic treatises. The manufacturing processes used in them have the following disadvantages, reducing their commercial value to a large extent.
1. A high temperature vacuum or controlled atmosphere furnace is necessary, resulting in an extremely high investment cost.
2. Sintering needs a temperature as high as 800-1200.degree. C., under a proper protective atmosphere (preventing oxidization), evidently increasing difficulty in manufacture.
3. Sintering powder materials in high temperature vacuum or atmosphere-controlled furnace slows the speed of production, and requires much electricity, resulting in high cost.